(1) Field of the Invention
The present invention relates to a hands-free telephone conversation system in which a local communication system connects a communication device and a relay device, wherein a user can communicate with the other party's communication device using the communication device.
The local communication system utilizes a short distance wireless communication method that enables adjacent devices to connect wirelessly at certain frequencies by, for example, Bluetooth®. Hereafter, the local communication system is used in this sense.
(2) Description of the Prior Art
Conventionally, there is a communication system that enables two communication devices to communicate by connecting wirelessly. When the wireless communication between these communication devices is blocked by a change of radio waves and so forth, there is a method, as a countermeasure, to send a substitute message to the other party's communication device through a network (for example, see Japanese Laid-Open Patent Application No. H11-146460).
FIG. 1 is a block diagram that shows a conventional structure of a communication system. The communication system comprises a communication device 1, a base station 2, a network 3 and the other party's communication device 4.
While the base station 2 includes a wireless communication unit 21, a central control unit 22, a cable communication unit 24, the other party's communication device 4 includes a voice input unit 41 and a voice output unit 42.
The prior communication system, which has the above-mentioned structure, operates as follows:
While the communication device 1 communicates wirelessly with the base station 2 by wireless communication unit 21, the base station 2 communicates with the other party's communication device 4 through the cable communication unit 23 and the network 3.
At the wireless communication path between the communication device 1 and the base station 2, when the wireless communication is in a normal state, the base station 2 receives voice signals from the communication device 1 by using the wireless communication unit 21, and sends the voice signals to the other party's communication device 4 by using the cable communication 23 and the network 3. The base station 2 also receives the voice signals from the other party's communication device 4 through the network 3 and by using the cable communication unit 23, and sends the voice signals to the communication device 1 by using the wireless communication unit 21. Thus, when the wireless communication path is in a normal state, a telephone conversation is realized.
On the other hand, at the above-mentioned wireless communication path, when it is impossible to use the wireless communication path because the status of radio waves has changed, or the communication device 1 is out of a wireless communication area of the base station 2, the base station 2 cannot detect the communication device 1 by using the wireless communication unit 21, and therefore, detects a disconnection of the wireless communication with the communication device 1 and processes the situation accordingly. Namely, when the base station 2 detects a disconnection of the wireless communication, the central control unit 22 produces an absent message like “It is impossible to communicate because the other party is out of the radio waves area.” that the message memory unit 24 memorizes beforehand, and instructs the cable communication unit 23 to send the absent message. The cable communication unit 23 then sends the absent message to the other party's communication device 4 through the network 3.
Thus, as a general rule, in the prior communication system that uses wireless communication, when it becomes impossible to use the wireless communication path, the base station 2 acts as a relay device, and sends the absent message to the other party's communication device 4.
Thus, in a hands-free telephone conversation system that comprises a communication device and a relay device that are connected through local wireless communication, it may be possible to use the above-mentioned measure when it is impossible to use the local wireless communication path.
However, it is not appropriate to apply the above-mentioned measure to disconnection of the communication path connected through a local wireless communication path in the afore-said hands-free telephone conversation system because there are many momentary disconnections in the communication path that is connected through local wireless communication. Generally speaking, a momentary disconnection means a very short power failure brought on by a thunderbolt and so forth. The momentary disconnection mentioned here means a very short disconnection of the local wireless communication path by a change in the status of radio waves and so forth.
In other words, in the local wireless communication path, the status of communication frequently changes from connection to short disconnection and then again to connection, and therefore, it may confuse the other party to send an absence message like “It is impossible to communicate because the other party is out of the radio waves area.” The other party may disconnect the telephone conversation although a relay device and the other party's communication device are able to establish a telephone conversation. Thus, the above-mentioned measure is not appropriate when a momentary disconnection occurs in the local wireless communication path. Especially, when the other party does not assume that the user is using the hands-free telephone conversation system that connects a communication device and a relay device, the other party cannot understand causes of interruption of communication and interruption of voice resulting from a momentary disconnection, so it is highly likely to cause a misunderstanding of the other party.
On the other hand, when measures are not taken when a momentary disconnection occurs in the local wireless communication path, there is a problem that the other party is inconvenienced because the momentary disconnection causes interruptions of communication and voice during a telephone conversation. Further, as was stated above, when the other party does not assume the use of the hands-free telephone conversation system, there is a problem that the other party's inconvenience can be greater.
Furthermore, because of a momentary disconnection in the communication path that is connected through local wireless communication, the status of the wireless communication becomes off and the connection does not recover within a short time, yet the telephone conversation between a relay device and a communication device goes on. Accordingly, there is a problem that the telephone charge will continue to increase.